Researchers over at the Fraunhofer Institute for Manufacturing, Engineering and Automation (IPA) in Germany have prototyped a new loudspeaker made using carbon nanotubes (CNTs). The concept was demonstrated last week at the Nano Tech 2010 show in Tokyo, Japan. Using CNTs, a simple and slim loudspeaker can be made without the need for components such as magnets and piezoelectric devices, enabling speakers to be placed in a variety of different locations.
The demonstration model measured 8cm x 6cm and was made simply by applying a conductive coating onto a PET (Polyethylene terephthalate) film, which contained CNTs. When a 12V direct voltage is applied to it, and the current is switched on and off rapidly, it generates an audio signal corresponding to the frequency of the switching.
“The principle of the sound generation is based on the thermoacoustic effect,” said a Fraunhofer IPA spokesperson. “The CNTs generate heat and expand when the current is on, and they cool down and shrink when the current is off.”
It is this expansion and contraction of the film that moves the air molecules and creates the resulting sound. The demo model is said to have a frequency response of 200Hz – 20kHz, so not really a sub woofer (yet).
The major benefit of the speaker is its extraordinary thinness. The demonstrated device was only 200 microns thick (about twice as thick as a human hair).This allows to be mounted on a number of flat surfaces such as wallpaper or advertising boards.
However researchers at the institute have also speculated that if fewer nanotubes could used in the film, it would be possible to make it completely transparent. Maybe the invisible loudspeaker is possible after all!